1. Field of the Invention
The present invention relates to a light emitting diode element (hereinafter referred to as a LED element) having a light emitting diode (hereinafter referred to LED) sealed by glass.
2. Discussion of Background
Heretofore, as a white light source, an incandescent bulb, a fluorescent lamp or the like has been widely used. In recent years, as a new type of white light source, a so-called white LED element has been developed, and its application to e.g. a backlight for liquid crystal display has been rapidly progressing.
In a presently commercially available typical one chip type white LED element, LED of a quantum well structure having a luminous layer of InGaN having In added to GaN, is sealed by a resin having a YAG phosphor.
This white LED element functions as a white light source as follows. Namely, when a direct current is conducted to LED, a blue light will be emitted from LED. On the other hand, the YAG phosphor will be excited by a part of the blue light, and a yellow light (fluorescence) will be emitted from this phosphor. Such blue light and yellow light are in a relation of complementary colors, and when they enter into human eyes in a mixed state, they will be observed as white light by the principle of an additive color mixture.
However, such a white LED element having LED sealed by a resin has had a problem such that when it is used for a long period of time, moisture tends to penetrate into the resin, whereby the operation of LED will be hindered, and by ultraviolet rays discharged from LED, the resin undergoes a color change, whereby its light transmittance tends to decrease.
As a white LED element to solve such a problem, JP-A-2002-203989 proposes at pages 2 to 7 one having LED formed on a substrate in a flip chip form, and such LED is sealed by sol-gel glass.
However, in such sol-gel glass, pores are present or tend to remain, whereby the hindrance by moisture of the LED operation may not sufficiently be suppressed. To solve such a problem of pores, heat treatment at 1,300° C. may typically be carried out, but there has been a problem that heat treatment at a very high temperature like 1,300° C. can not be applied to the production of a LED element.